1. Field of the Invention
The present invention relates to an ultrasonic diagnostic system and a system and a method for ultrasonic imaging wherein the velocity of biological tissue such as cardiac muscle is estimated, and the estimated velocity information is processed to output local motion information of the tissue, thereby providing information useful in medical diagnosis, and in particular, it relates to a method for reducing the time and labor for operation by automatically detecting an end systole phase.
2. Description of the Related Art
Objective and quantitative evaluation of functions of biological tissue is generally very important for diagnosis of biological tissue such as cardiac muscle. Diagnostic imaging using an ultrasonic imaging system also tries various quantitative evaluations principally for hearts as an example. A typical example is tissue tracking imaging (TTI) method (e.g., refer to Patent Document 1). The TTI method allows quantitative evaluation by local-wall-motion indices such as distortion and displacement using tissue velocity.
To find distortion or displacement using tissue velocity, time quadrature is required, as described in Patent Document 1. Since the result of time quadrature depends on an integration interval (time), the importance of the setting of the interval will easily be understood.
Of particular importance is a start phase. When integration start phase is, for example, in an end diastole phase, systolic distortion and displacement can be analyzed. Paying attention to distortion, normal cardiac muscle is thickened in the wall thickness direction (the minor axis), and shortened along the major axis during systole. In contrast, when the integration start phase is in end systole phase, diastolic distortion and displacement can be analyzed. Also paying attention to distortion, normal cardiac muscle is thinned in the wall thickness direction (the minor axis), and stretched along the major axis during systole.
Furthermore, integration end time is important second to the start time phase as a time phase that reflects the final state of distortion and displacement in specified intervals such as systole and diastole. Specifically, the most common way will be that the state of the whole motion by time quadrature for systole is analyzed in an end systole phase, and the state of the whole motion by time quadrature for diastole is analyzed in an end diastole phase.
To determine the integration interval for systole or diastole for a variety of applications, the end diastole phase and the end systole phase must be provided as accurately as possible. To enhance simplicity of the analyzing process, it is desirable that the two time phases of end diastole phase and end systole phase be set automatically. Furthermore, a technique of monopolar display of distortion is disclosed in JP-A-2003-175041, for example, as another unique application setting other than the setting of an integration interval in each phase interval of systole and diastole. To realize accurate and simple time phase setting is also very useful for the distortion monopolar display.
Of the end diastole phase and the end systole phase, the end diastole phase can be detected automatically as an R-wave phase in an electrocardiogram. On the other hand, the end systole phase cannot easily be detected from an electrocardiogram; however, the following automatic setting technique is known.
With stress echo packages, which are recently becoming widespread, only systoles are often cut out from a series of moving images, and are analyzed. In this case, a specified interval (duration time DT [sec]) from R wave can be set. Specifically speaking, a DT phase corresponds to an end systole phase. It is known that DTs vary depending on heart rates (HR) [bpm] (DTs decrease generally as HRs increase). Accordingly, DTs can often be set by users as a table for each HR.
Despite such devised stress echo packages, the accuracy required for an end systole phase being set is so low to be determined uniquely by a predetermined time in advance. Thus, since it has not a structure determined to the motion of a signal source, e.g., it is not necessarily a high-accuracy setting method for an end systole phase. Accordingly, this has the disadvantage of low time accuracy in view of automatically setting intervals of time quadrature for finding distortion or displacement.
Furthermore, a technique of automatically recognizing an end systole phase using a cardiac-cavity volume/area or cardiac sound graph by automated contour tracking (ACT) method is recently disclosed (e.g., refer to Patent Document 2). As shown in the document, it is generally known that “an end systole phase in clinical term is the time when the second sound on a phonocardiogram is generated”. However, it is difficult to stably detect only the second sound from a phonocardiogram waveform having many abrupt changes, and there can be also some cases in which a phonocardiogram cannot always be provided at examinations (because many cardiac ultrasonic examinations use only phonocardiograms as reference signals). The technique by the ACT method discloses “finding an end systole phase as a time phase in which the area or volume of a cardiac cavity is minimized” by estimating the area or volume of a cardiac cavity from positional information on endocardium that is automatically detected.